Deleted instance will reappear and get rebuilt in an unfortunate sequence of events

This issue has been observed in a customer setup. The sequence of events is as follows:

Pull in the patch: https://review.couchbase.org/c/indexing/+/213169 for easy repro

a. create index idx_1 on default(name) with {"nodes":["127.0.0.1:9001"]}

b. alter index idx_1 on default with {"action":"replica_count", "num_replica": 1}

c. Due to the above patch, build during alter index will fail on node n2

d. Drop the replica on node n2 (9002) with the below command:

alter index idx_1 on default with {"action":"replica_count", "num_replica": 0}

e. After 3 min, on node n2, the replica is created again

The issue is due to node n1 removing the drop index token while create token exists in metaKV. The check for create token only considers index defnID as key. However, for alter index, both requestID and index definition ID are used. Therefore, both defnID requestID are to be considered when checking the presence of create command token during drop instance token check.